Fan

ABSTRACT

A fan includes a motor and an impeller. The motor includes a stationary portion and a rotating portion rotatably supported by the stationary portion. The stationary portion includes a stator and a bearing portion arranged inside of the stator. The rotating portion includes a rotor magnet arranged radially outside the stator; a shaft inserted in the bearing portion, and having an upper portion fixed to the impeller directly or through one or more members; and a thrust portion arranged axially opposite the bearing portion, and including an annular surface arranged around the shaft.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fan arranged to produce air currents.

2. Description of the Related Art

Fans have often been used as cooling fans arranged to cool electroniccomponents inside cases of a variety of electronic devices. A motorportion of a blower fan disclosed in JP-A 2009-213225 includes a baseportion, an armature, a substantially cylindrical bearing supportportion, two ball bearings, and a rotor portion. The bearing supportportion is fixed in a center of the base portion. The two ball bearingsare fixed to an inside surface of the bearing support portion, while thearmature is fixed to an outside surface of the bearing support portion.A shaft is inserted in the ball bearings, so that the rotor portion issupported to be rotatable with respect to the bearing support portion.The base portion includes an annular groove defined therein which isarranged to surround a circumference of the bearing support portion. Ahelical coil spring is disposed in this groove. An upper end portion ofthe coil spring is arranged to be in axial contact with an insulator ofthe armature. Thus, vibrations of the armature are absorbed by the coilspring during rotation of the rotor portion, so that vibrations of theblower fan are reduced.

A bearing apparatus used in a spindle motor disclosed in JP-A2005-155912 includes a shaft, a thrust plate, a sleeve, and a housingarranged in the shape of a cylinder with a bottom. The shaft is insertedin the sleeve. The housing is arranged to accommodate the sleeve. Thethrust plate is arranged at a lower end portion of the shaft. An innercircumferential surface of the sleeve includes dynamic pressuregenerating grooves defined therein, and a radial dynamic pressurebearing is defined between an outer circumferential surface of the shaftand the inner circumferential surface of the sleeve. Each of a lower endsurface of the sleeve and an upper surface of a bottom portion of thehousing includes thrust dynamic pressure generating grooves definedtherein. Thrust dynamic pressure bearings are defined between the lowerend surface of the sleeve and an upper surface of the thrust plate, andbetween a lower surface of the thrust plate and the upper surface of thebottom portion of the housing.

A cooling fan disclosed in US 2008/0278911 includes a base portion, abearing portion, a fluid dynamic bearing, a coil assembly, and animpeller.

SUMMARY OF THE INVENTION

In recent years, electronic devices, such as servers, have improved inperformance, and the amount of heat generated from the electronicdevices has increased accordingly. There is therefore a demand for fansin the electronic devices to be rotated at higher speeds in order toincrease air volume. However, an increase in the rotation speed of thefans leads to greater vibrations of the fans, and this will affect otherdevices in the electronic devices. For example, vibrations of a fan maycause an error in reading or writing by a disk drive apparatus.

A primary advantage of the present invention is to reduce vibrations ofa fan.

A fan according to a preferred embodiment of the present inventionincludes a motor and an impeller including a plurality of blades, andarranged to rotate about a central axis through the motor to produce aircurrents. The motor includes a stationary portion and a rotating portionrotatably supported by the stationary portion. The stationary portionincludes a stator and a bearing portion arranged inside of the stator.The rotating portion includes a rotor magnet arranged radially outsidethe stator; a shaft inserted in the bearing portion, and having an upperportion fixed to the impeller directly or through one or more members;and a thrust portion arranged axially opposite the bearing portion, andincluding an annular surface arranged around the shaft. A radial dynamicpressure bearing portion arranged to generate a fluid dynamic pressurein a lubricating oil is defined in a radial gap defined between an innercircumferential surface of the bearing portion and an outercircumferential surface of the shaft, while a thrust dynamic pressurebearing portion arranged to generate a fluid dynamic pressure in thelubricating oil is defined in a thrust gap defined between the annularsurface and a surface of the bearing portion which is axially opposed tothe annular surface. A single seal gap arranged in an annular shape andcentered on the central axis is defined between the stationary androtating portions. The seal gap, the radial gap, and the thrust gap arearranged to together define a single continuous bladder structure, thelubricating oil is arranged continuously in the bladder structure, and asurface of the lubricating oil is defined only in the seal gap.

The present invention enables the fan to achieve reduced vibration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a fan according to a first preferredembodiment of the present invention.

FIG. 2 is a cross-sectional view of a bearing mechanism according to thefirst preferred embodiment.

FIG. 3 is a cross-sectional view illustrating a portion of the bearingmechanism in an enlarged form.

FIG. 4 is a cross-sectional view illustrating a portion of the bearingmechanism in an enlarged form.

FIG. 5 is a cross-sectional view of a bearing portion according to thefirst preferred embodiment.

FIG. 6 is a bottom view of the bearing portion.

FIG. 7 is a plan view of a thrust cap according to the first preferredembodiment.

FIG. 8 is a graph showing a result of a simulation of vibration thatoccurs in the fan.

FIG. 9 is a graph showing a result of a simulation of vibration thatoccurs in the fan.

FIG. 10 is a graph showing a result of a simulation of vibration thatoccurs in the fan.

FIG. 11 is a graph showing a result of a simulation of vibration thatoccurs in the fan.

FIG. 12 is a graph showing a result of a simulation of vibration thatoccurs in a fan as a comparative example.

FIG. 13 is a cross-sectional view of a bearing mechanism according to amodification of the first preferred embodiment.

FIG. 14 is a cross-sectional view illustrating a portion of the bearingmechanism in an enlarged form.

FIG. 15 is a cross-sectional view of a fan according to a secondpreferred embodiment of the present invention.

FIG. 16 is a cross-sectional view of a motor according to the secondpreferred embodiment.

FIG. 17 is a cross-sectional view of a bearing mechanism according tothe second preferred embodiment.

FIG. 18 is a cross-sectional view illustrating a portion of the bearingmechanism.

FIG. 19 is a cross-sectional view of a motor according to a modificationof the second preferred embodiment.

FIG. 20 is a cross-sectional view of a motor according to anothermodification of the second preferred embodiment.

FIG. 21 is a cross-sectional view of a motor according to yet anothermodification of the second preferred embodiment.

FIG. 22 is a cross-sectional view of a motor according to yet anothermodification of the second preferred embodiment.

FIG. 23 is a cross-sectional view of a fan according to a thirdpreferred embodiment of the present invention.

FIG. 24 is a cross-sectional view of a motor according to the thirdpreferred embodiment.

FIG. 25 is a cross-sectional view of a bearing mechanism according tothe third preferred embodiment.

FIG. 26 is a cross-sectional view of a motor according to a modificationof the third preferred embodiment.

FIG. 27 is a cross-sectional view of a motor according to anothermodification of the third preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is assumed herein that a vertical direction is defined as a directionin which a central axis of a motor extends, and that an upper side and alower side along the central axis in FIG. 1 are referred to simply as anupper side and a lower side, respectively. It should be noted, however,that the above definitions of the vertical direction and the upper andlower sides should not be construed to restrict relative positions ordirections of different members or portions when the motor is actuallyinstalled in a device. Also note that a direction parallel to thecentral axis is referred to by the term “axial direction”, “axial”, or“axially”, that radial directions centered on the central axis aresimply referred to by the term “radial direction”, “radial”, or“radially”, and that a circumferential direction about the central axisis simply referred to by the term “circumferential direction”,“circumferential”, or “circumferentially”.

First Preferred Embodiment

FIG. 1 is a cross-sectional view of an axial fan 1 according to a firstpreferred embodiment of the present invention. Hereinafter, the axialfan 1 will be referred to simply as the “fan 1”. The fan 1 includes amotor 11, an impeller 12, a housing 13, a plurality of support ribs 14,and a base portion 15. The housing 13 is arranged to surround an outercircumference of the impeller 12. The housing 13 is joined to the baseportion 15 through the support ribs 14. The support ribs 14 are arrangedin a circumferential direction. The base portion 15 is definedintegrally with the support ribs 14. The motor 11 is fixed on the baseportion 15.

The impeller 12 is made of a resin, and includes a cup 121 and aplurality of blades 122. The cup 121 is arranged substantially in theshape of a covered cylinder. The cup 121 is arranged to cover an outsideof the motor 11. The cup 121 is arranged to define a portion of arotating portion 2 of the motor 11. The rotating portion 2 will bedescribed below. The cup 121 includes a top face portion 123 and a sidewall portion 124. The top face portion 123 is arranged to spreadperpendicularly to a central axis J1. The side wall portion 124 isarranged to extend downward from an outer edge portion of the top faceportion 123. The blades 122 are arranged to extend radially outward froman outer circumferential surface of the side wall portion 124 with thecentral axis J1 as a center. The cup 121 and the blades 122 are definedintegrally with each other by a resin injection molding process.

A hole portion 125 is defined in an upper surface of the top faceportion 123. A weight 129 is arranged in the hole portion 125. Theweight 129 is an adhesive including a metal having a high specificgravity, such as tungsten. Another weight 129 is arranged on a lower endportion 124 a of the side wall portion 124 on a radially inner sidethereof. A reduction in unbalance of each of the impeller 12 and therotating portion 2 of the motor 11 can be achieved by arranging theweight 129 on each of an upper portion and a lower portion of theimpeller 12. The reduction in the unbalance leads to a reduction invibrations of the fan 1 owing to a displacement of a center of gravityof any of the impeller 12 and the motor 11 from the central axis J1.Hereinafter, the hole portion 125 and the lower end portion 124 a of theside wall portion 124, on each of which the weight 129 is arranged, willbe referred to as “balance correction portions 125 and 124 a”,respectively.

The impeller 12 of the fan 1 is caused by the motor 11 to rotate aboutthe central axis J1 to produce downward air currents.

The motor 11 is a three-phase outer-rotor motor. The motor 11 includesthe rotating portion 2, a stationary portion 3, and a bearing mechanism4. The rotating portion 2 includes a substantially cylindrical metallicyoke 21, a rotor magnet 22, and the cup 121. The yoke 21 is fixed to aninside of the cup 121. The rotor magnet 22 is fixed to an innercircumferential surface of the yoke 21. The rotating portion 2 issupported through the bearing mechanism 4 to be rotatable about thecentral axis J1 with respect to the stationary portion 3.

The stationary portion 3 includes a substantially cylindrical bearingsupport portion 31, a stator 32, and a circuit board 33. A lower portionof the bearing support portion 31 is fixed to an inner circumferentialsurface of the base portion 15 which defines a central hole portionthereof. The stator 32 is fixed to an outer circumferential surface ofthe bearing support portion 31 on an upper side of the base portion 15.The stator 32 is arranged radially inside the rotor magnet 22. Thestator 32 includes a stator core 321 and a plurality of coils 322arranged on the stator core 321. The stator core 321 is defined bylaminated steel sheets. The circuit board 33 is fixed below the stator32. Lead wires from the coils 322 are attached to pins (not shown)inserted in holes of the circuit board 33, whereby the stator 32 and thecircuit board 33 are electrically connected with each other. Note thatthe lead wires from the coils 322 may be directly connected to thecircuit board 33. While the motor 11 is driven, a turning force isgenerated between the rotor magnet 22 and the stator 32.

An annular magnetic member 331 is arranged on an upper surface of thecircuit board 33. The magnetic member 331 is arranged under the rotormagnet 22. While the motor 11 is stationary, a magnetic center of thestator 32 is located at a level lower than that of a magnetic center ofthe rotor magnet 22. In the fan 1, magnetic attraction forces thatattract the rotor magnet 22 downward are generated between the rotormagnet 22 and the stator 32, and between the rotor magnet 22 and themagnetic member 331. A force that acts to lift the impeller 12 relativeto the stationary portion 3 during rotation of the fan 1 is therebyreduced.

The bearing mechanism 4 includes a shaft 41, an annular thrust plate 42,a bearing portion 44, a thrust cap 45, i.e., a cap member, and alubricating oil 46. The top face portion 123 of the impeller 12 isindirectly fixed to an upper portion of the shaft 41 through a bushing25 made of a metal. The thrust plate 42 is a thrust portion arrangedaxially opposite the bearing portion 44, and fixed to a lower portion ofthe shaft 41. The thrust plate 42 is arranged to extend radially outwardfrom a lower end portion of the shaft 41. The bearing portion 44 isarranged radially inside the stator 32. Note that each of the shaft 41and the thrust plate 42 defines a portion of the rotating portion 2,while each of the bearing portion 44 and the thrust cap 45 defines aportion of the stationary portion 3. The same is true of other preferredembodiments of the present invention described below.

FIG. 2 is a cross-sectional view of a lower portion of the bearingmechanism 4 and its vicinity in an enlarged form. An innercircumferential surface of the thrust plate 42 includes a groove portion421 arranged to extend in an axial direction, and a communicating hole421 a is defined between the groove portion 421 and an outercircumferential surface 411 of the shaft 41. This contributes toreducing a difference in internal pressure of the lubricating oil 46between an upper side and a lower side of the thrust plate 42. Referringto FIG. 3, an upper surface of the thrust plate 42 includes an inclinedsurface 422 a defined in an outer edge portion thereof. The inclinedsurface 422 a is arranged to be inclined downward with increasingdistance from the central axis J1. A portion of the upper surface of thethrust plate 42 which is radially inward of the inclined surface 422 ais an annular surface perpendicular to the central axis J1 and arrangedaround the shaft 41. Hereinafter, this portion of the upper surface ofthe thrust plate 42 will be referred to as an “upper annular surface422”. A lower surface of the thrust plate 42 includes an inclinedsurface 423 a arranged to be inclined upward with increasing distancefrom the central axis J1. A portion of the lower surface of the thrustplate 42 which is radially inward of the inclined surface 423 a is anannular surface perpendicular to the central axis J1. Hereinafter, thisportion of the lower surface of the thrust plate 42 will be referred toas a “lower annular surface 423”.

The bearing portion 44 illustrated in FIG. 2 is a single sleeve made ofa metal, such as stainless steel or phosphor bronze. The bearing portion44 is fixed to an inner circumferential surface of the bearing supportportion 31. The shaft 41 is inserted in the bearing portion 44. Thebearing portion 44 includes a first shoulder portion 442 defined by anincrease in the diameter of an inner circumferential surface 441 of thebearing portion 44 in a lower portion of the inner circumferentialsurface 441, and a second shoulder portion 443 defined by an increase inthe diameter of the inner circumferential surface 441 between the firstshoulder portion 442 and a lower end portion 444 of the bearing portion44. The thrust cap 45 is arranged inside of the lower end portion 444,and an outer circumferential surface of the thrust cap 45 is fixed to aninner circumferential surface of the lower end portion 444. The thrustcap 45 is arranged to close a bottom portion of the bearing portion 44.An outer edge portion of an upper surface 451 of the thrust cap 45 isarranged to be in axial contact with a lower surface 443 a of the secondshoulder portion 443, that is, a surface having a normal orienteddownward. The thrust plate 42 is arranged between the first shoulderportion 442 and the second shoulder portion 443.

In the bearing mechanism 4, a radial gap 51 is defined between the innercircumferential surface 441 of the bearing portion 44 and the outercircumferential surface 411 of the shaft 41. A gap 52 is defined betweenthe upper annular surface 422 of the thrust plate 42 and a lower surface442 a of the first shoulder portion 442, which is arranged axiallyopposite the upper annular surface 422, that is, a surface having anormal oriented downward in the axial direction. Hereinafter, the gap 52will be referred to as a “first lower thrust gap 52”. The lower annularsurface 423 of the thrust plate 42 and the upper surface 451 of thethrust cap 45 are arranged axially opposite each other, and a gap 53 isdefined between the lower annular surface 423 and the upper surface 451.Hereinafter, the gap 53 will be referred to as a “second lower thrustgap 53”. The sum of the axial width of the first lower thrust gap 52 andthe axial width of the second lower thrust gap 53 is arranged in therange of about 10 μm to about 40 μm. A gap 54 is defined between anouter circumferential surface of the thrust plate 42 and a portion ofthe inner circumferential surface 441 of the bearing portion 44 which isradially opposed to the outer circumferential surface of the thrustplate 42. Hereinafter, the gap 54 will be referred to as a “side gap54”.

FIG. 4 is a diagram illustrating an upper portion of the bearing portion44 and its vicinity in an enlarged form. An upper portion of the innercircumferential surface 441 of the bearing portion 44 includes a firstinclined surface 441 a and a second inclined surface 441 b. The firstinclined surface 441 a is arranged to extend radially inward andobliquely downward from an upper surface of the bearing portion 44. Inother words, the diameter of the first inclined surface 441 a isarranged to gradually increase with increasing height. The secondinclined surface 441 b is arranged to extend radially inward andobliquely downward from a lower end of the first inclined surface 441 a.In other words, the diameter of the second inclined surface 441 b isarranged to gradually increase with increasing height. An angle definedby the first inclined surface 441 a with the central axis J1 is arrangedto be greater than an angle defined by the second inclined surface 441 bwith the central axis J1. A boundary between the first and secondinclined surfaces 441 a and 441 b is arranged radially inward of aradial middle point between an upper end of the first inclined surface441 a and the outer circumferential surface 411 of the shaft 41.

The first inclined surface 441 a and the outer circumferential surface411 of the shaft 41 are arranged to together define a single seal gap 55arranged to gradually increase in radial width with increasing height.The seal gap 55 is arranged in an annular shape and centered on thecentral axis J1. A seal portion 55 a arranged to retain the lubricatingoil 46 through capillary action is defined in the seal gap 55. The sealgap 55 serves also as an oil buffer arranged to hold the lubricating oil46. In the motor 11, the seal gap 55, the radial gap 51 illustrated inFIG. 2, the first lower thrust gap 52, the side gap 54, and the secondlower thrust gap 53 are arranged to together define a single continuousbladder structure 5. The lubricating oil 46 is arranged continuously inthe bladder structure 5. Within the bladder structure 5, a surface ofthe lubricating oil 46 is defined only in the seal gap 55 illustrated inFIG. 4.

The upper surface of the bearing portion 44 and a lower surface of thebushing 25, which is fixed to the upper portion of the shaft 41, arearranged to together define a gap 501 extending radially therebetween.An outer circumferential surface of the bushing 25 and the innercircumferential surface of the bearing support portion 31 are arrangedto together define a gap 502 extending in the axial directiontherebetween. The seal portion 55 a is arranged to be in communicationwith an exterior space through the gaps 501 and 502. Here, the exteriorspace refers to a space above the stator 32 as illustrated in FIG. 1.Provision of the gaps 501 and 502 contributes to preventing an airincluding a lubricating oil evaporated from the seal portion 55 a fromtraveling out of the bearing mechanism 4. This contributes to reducingevaporation of the lubricating oil 46 out of the bearing mechanism 4.

FIG. 5 is a vertical cross-sectional view of the bearing portion 44. Theupper portion and the lower portion of the inner circumferential surface441 of the bearing portion 44 include a first radial dynamic pressuregroove array 711 and a second radial dynamic pressure groove array 712,respectively, defined therein. Each of the first and second radialdynamic pressure groove arrays 711 and 712 is arranged in a herringbonepattern. An outer circumferential surface of the bearing portion 44includes minute recessed portions defined therein. The minute recessedportions are arranged axially between the first and second radialdynamic pressure groove arrays 711 and 712. Referring to FIG. 2, in anupper portion of the radial gap 51, an upper radial dynamic pressurebearing portion 681 arranged to generate a radial fluid dynamic pressureacting on the lubricating oil 46 is defined through the first radialdynamic pressure groove array 711. In a lower portion of the radial gap51, a lower radial dynamic pressure bearing portion 682 arranged togenerate a radial fluid dynamic pressure acting on the lubricating oil46 is defined through the second radial dynamic pressure groove array712. Hereinafter, the upper and lower radial dynamic pressure bearingportions 681 and 682 will be referred to collectively as a “radialdynamic pressure bearing portion 68”. The radial dynamic pressurebearing portion 68 is arranged axially between the two balancecorrection portions 124 a and 125 illustrated in FIG. 1. In addition,the upper radial dynamic pressure bearing portion 681 is arranged tooverlap with the center of gravity of each of the motor 11 and theimpeller 12 in a radial direction.

FIG. 6 is a bottom view of the bearing portion 44. The lower surface 442a of the first shoulder portion 442 includes a first thrust dynamicpressure groove array 721 arranged in the herringbone pattern. FIG. 7 isa plan view of the thrust cap 45. The upper surface 451 of the thrustcap 45, that is, a bottom surface of the bladder structure 5 illustratedin FIG. 2, includes a second thrust dynamic pressure groove array 722arranged in the herringbone pattern. Referring to FIG. 2, in the firstlower thrust gap 52, a first lower thrust dynamic pressure bearingportion 691 arranged to generate an axial fluid dynamic pressure actingon the lubricating oil 46 is defined through the first thrust dynamicpressure groove array 721. In other words, the first lower thrustdynamic pressure bearing portion 691 is defined by the upper annularsurface 422 of the thrust plate 42, which corresponds to anupward-facing thrust dynamic pressure bearing surface, and the lowersurface 442 a of the first shoulder portion 442, which corresponds to adownward-facing thrust dynamic pressure bearing surface. In addition, inthe second lower thrust gap 53, a second lower thrust dynamic pressurebearing portion 692 arranged to generate an axial fluid dynamic pressureacting on the lubricating oil 46 is defined through the second thrustdynamic pressure groove array 722.

While the motor 11 is driven, the shaft 41 is supported in the radialdirection by the radial dynamic pressure bearing portion 68, and thethrust plate 42 is supported in the axial direction by the first andsecond lower thrust dynamic pressure bearing portions 691 and 692. As aresult, the rotating portion 2 and the impeller 12 illustrated in FIG. 1are supported to be rotatable with respect to the stationary portion 3.While the motor 11 is driven, the lubricating oil 46 circulates throughthe first lower thrust gap 52, the side gap 54, the second lower thrustgap 53, and the communicating hole 421 a illustrated in FIG. 2. Inaddition, the inclined surface 422 a is defined in the outer edgeportion of the upper surface of the thrust plate 42 as illustrated inFIG. 3, and this contributes to preventing the thrust plate 42 fromcoming into hard contact with the lower surface 442 a of the firstshoulder portion 442 of the bearing portion 44 even when the shaft 41 istilted.

Referring to FIG. 5, a portion of the first radial dynamic pressuregroove array 711 is defined in a lower portion of the second inclinedsurface 441 b. Referring to FIG. 4, when the shaft 41 is slightly tiltedwhile the fan 1 is driven, a fluid dynamic pressure is generated by thefirst radial dynamic pressure groove array 711 in a gap 56 definedbetween a portion of the outer circumferential surface 411 of the shaft41 which approaches the second inclined surface 441 b and a portion ofthe second inclined surface 441 b which is opposed to this portion ofthe outer circumferential surface 411. As a result, the shaft 41 issupported by the second inclined surface 441 b. Thus, when the shaft 41is tilted during rotation of the rotating portion 2, the second inclinedsurface 441 b extends along the outer circumferential surface 411 of theshaft 41 in the gap 56, which is located below and adjacent to the sealgap 55. The shaft 41 is thus prevented from coming into hard contactwith the upper portion of the bearing portion 44.

FIG. 8 is a graph showing a result of a simulation of vibration thatoccurs in the fan 1 in the case where the radial width of the radial gap51 is 3 μm. A horizontal axis represents frequencies of the vibration,while a vertical axis represents the amplitude of each frequencycomponent of the vibration. FIGS. 9, 10, and 11 are graphs showingresults of simulations of vibration that occurs in the fan 1 in the casewhere the radial width of the radial gap 51 is 4 μm, 5 μm, and 6 μm,respectively. FIG. 12 is a graph showing a result of a simulation ofvibration that occurs in a fan as a comparative example in which a motorincluding a ball bearing is installed.

As indicated by a curve 90 in FIG. 12, in the case of the vibration thatoccurs in the fan including the ball bearing, a plurality of peaks occurin the range of 750 Hz to 1250 Hz. In FIG. 12, the peaks are denoted,from right to left, by reference numerals 901, 902, 903, and 904,respectively. In contrast, referring to FIGS. 8 and 9, in the case ofthe bearing mechanisms 4 in which the width of the radial gap is 3 μmand 4 μm, respectively, corresponding peaks 911, 912, 913, and 914 arelower than the peaks 901, 902, 903, and 904, respectively, in FIG. 12.Further, referring to FIGS. 10 and 11, in the case of the bearingmechanisms 4 in which the width of the radial gap 51 is 5 μm and 6 μm,respectively, peaks do not occur at positions corresponding to those ofthe peaks 901 and 904 on the far right and on the far left,respectively, in FIG. 12. Moreover, peaks 912 and 913 corresponding tothe remaining peaks 902 and 903, respectively, are less than half ashigh as the peaks 902 and 903, respectively.

As described above, the fan 1 is able to achieve reduced vibration ascompared to known fans in which ball bearings are used. This is due to aso-called damper effect produced by the lubricating oil 46 between theshaft 41 and the bearing portion 44. In particular, a satisfyingreduction in the vibration can be achieved when the radial width of theradial gap 51 is 5 μm or greater. The radial width of the radial gap 51is arranged to be 20 μm or less in order to generate a sufficient fluiddynamic pressure in the radial gap 51. More preferably, the width of theradial gap 51 is arranged in the range of about 5 μm to about 10 μm.

The fan 1 according to the first preferred embodiment has been describedabove. Use of the bearing mechanism 4, which is a fluid dynamic bearingmechanism, in the fan 1 contributes to reducing the vibrations of thefan 1. The reduction in the vibrations of the fan 1 leads to a reductionin power consumption of the fan 1. In addition, the motor 11 can bemanufactured at a lower cost than a comparable motor in which a ballbearing is used.

In the case of a fluid dynamic bearing mechanism in which seal portionsare defined in an upper portion and a lower portion of a bearing portionthereof, a sophisticated design is required to prevent a difference inpressure between the seal portions from causing a leakage of thelubricating oil 46. In contrast, the bearing mechanism 4 of the motor 11has a so-called full-fill structure, including only one seal portion 55a, and it is therefore easy to prevent a leakage of the lubricating oil46 in the case of the bearing mechanism 4. In addition, the surface ofthe lubricating oil 46 in the seal portion 55 a can be maintained at asubstantially fixed position. Moreover, a reduction in evaporation ofthe lubricating oil 46 is achieved compared to the case where aplurality of seal portions are provided. In particular, because the sealportion 55 a is arranged in an inner portion of the motor 11, the sealportion 55 a is not exposed to air currents while the fan 1 is driven. Afurther reduction in the evaporation of the lubricating oil 46 isthereby achieved. Furthermore, entry of an extraneous material into theseal portion 55 a can be prevented. In the bearing mechanism 4, becausethe seal portion 55 a is defined around the shaft 41, a leakage of thelubricating oil 46 out of the seal portion 55 a owing to a centrifugalforce can be prevented more effectively than in the case where the sealportion is arranged away from and radially outward of the shaft 41.

Because the sum of the axial width of the first lower thrust gap 52 andthe axial width of the second lower thrust gap 53 is arranged in therange of about 10 μm to about 40 μm, the fluid dynamic pressures can begenerated while ensuring the damper effect owing to the lubricating oil46.

Because the second inclined surface 441 b in which a portion of thefirst radial dynamic pressure groove array 711 is defined is arranged inthe inner circumferential surface 441 of the bearing portion 44, it ispossible to support the shaft 41 sufficiently even if the radial gap 51is widened. Consequently, it is possible to prevent a reduction inbearing rigidity even when the fan 1 is caused to rotate at a high speedor in a high-temperature condition.

Because the motor 11 is a three-phase motor, the motor 11 is capable ofbeing rotated at a high speed. It is therefore easy to cause thefrequencies of the vibration that can occur in the motor 11 to deviatefrom a frequency band that may affect another device in an electronicdevice in which the fan 1 is installed.

The magnetic member 331 provided in the motor 11 generates the magneticattraction force that attracts the rotor magnet 22 downward. Thiscontributes to reducing an increase in a bearing loss that occurs in thefirst lower thrust dynamic pressure bearing portion 691, while the fan 1is driven, owing to the force that acts to lift the impeller 12 relativeto the stationary portion 3. Moreover, the additional magneticattraction force that attracts the rotor magnet 22 downward is generatedbecause the magnetic center of the stator 32 is arranged at a levellower than that of the magnetic center of the rotor magnet 22. Thiscontributes to further reducing the increase in the bearing loss thatoccurs in the first lower thrust dynamic pressure bearing portion 691.

Because the radial dynamic pressure bearing portion 68 is arrangedaxially between the two balance correction portions 124 a and 125, eachof the rotating portion 2 and the impeller 12 is capable of stablerotation, and a further reduction in the vibrations is thereby achieved.In addition, it is possible to reduce the axial length of the radialdynamic pressure bearing portion 68, and to shorten the bearing portion44. This makes it possible to manufacture the bearing portion 44 withhigh precision. The axial length of the bearing portion 44 is preferablyarranged to be less than about four times the diameter of the bearingportion 44. Because the upper radial dynamic pressure bearing portion681 is arranged to overlap with the center of gravity of each of themotor 11 and the impeller 12 in the radial direction, stability of therotation of each of the rotating portion 2 and the impeller 12 isincreased, and a further reduction in the vibrations is therebyachieved. The same is true of other preferred embodiments of the presentinvention described below.

FIG. 13 is a cross-sectional view of a bearing mechanism 4 according toa modification of the first preferred embodiment. A bearing portion 44 aof the bearing mechanism 4 includes a tubular sleeve 47 and a bearinghousing 48. The sleeve 47 is defined by a metallic sintered body. Thesleeve 47 is impregnated with a lubricating oil 46. The bearing housing48 is arranged to cover an outer circumferential surface of the sleeve47. The bearing housing 48 includes an annular upper portion 481arranged to extend radially inward on an upper side of the sleeve 47. Acirculation hole arranged to extend in the axial direction is definedbetween the sleeve 47 and the bearing housing 48. The lubricating oil 46is arranged to circulate through the circulation hole, a gap definedbetween a lower surface of the annular upper portion 481 and an uppersurface of the sleeve 47, a radial gap 51, and a first lower thrust gap52.

Referring to FIG. 14, an inner circumferential surface 481 a of theannular upper portion 481 is an inclined surface whose diametergradually increases with increasing height. In other words, the innercircumferential surface 481 a is arranged to be inclined radially inwardwith decreasing height. Hereinafter, the inner circumferential surface481 a will be referred to as a “first inclined surface 481 a”. An upperportion of an inner circumferential surface 471 of the sleeve 47includes an inclined surface 471 a whose diameter gradually increaseswith increasing height. In other words, the inclined surface 471 a isarranged to be inclined radially inward with decreasing height.Hereinafter, the inclined surface 471 a will be referred to as a “secondinclined surface 471 a”. An angle defined by the first inclined surface481 a with a central axis J1 is arranged to be greater than an angledefined by the second inclined surface 471 a with the central axis J1.The bearing mechanism 4 according to the present modification of thefirst preferred embodiment is otherwise similar in structure to thebearing mechanism 4 illustrated in FIG. 2.

A seal gap 55 arranged to gradually increase in radial width withincreasing height is defined between the first inclined surface 481 aand an outer circumferential surface 411 of a shaft 41. Adjacent to andbelow the seal gap 55, a gap 56 is defined between the outercircumferential surface 411 of the shaft 41 and the second inclinedsurface 471 a. A seal portion 55 a arranged to retain the lubricatingoil 46 through capillary action is defined in the seal gap 55. Becausethe seal portion 55 a is defined around the shaft 41, a leakage of thelubricating oil 46 out of the seal portion 55 a due to a centrifugalforce is prevented.

A portion of a first radial dynamic pressure groove array 711 similar tothe first radial dynamic pressure groove array 711 illustrated in FIG. 5is defined in a lower portion of the second inclined surface 471 a. Whenthe shaft 41 is slightly tilted while a fan 1 is driven, the secondinclined surface 471 a extends along the outer circumferential surface411 of the shaft 41, so that a fluid dynamic pressure is generated inthe gap 56. The shaft 41 is thereby supported by the second inclinedsurface 471 a so that the shaft 41 can be prevented from coming intohard contact with an upper portion of the bearing portion 44 a.

Second Preferred Embodiment

FIG. 15 is a cross-sectional view of a fan 1 a according to a secondpreferred embodiment of the present invention. The fan 1 a includes amotor 11 a and a support portion 16. The motor 11 a has a structuredifferent from that of the motor 11 illustrated in FIG. 1. The fan 1 ais otherwise similar in structure to the fan 1 according to the firstpreferred embodiment. Accordingly, like members or portions aredesignated by like reference numerals, and redundant description isomitted. The support portion 16 is substantially columnar in shape, andis arranged to support the motor 11 a from below. A lower portion of thesupport portion 16 is fixed to a hole portion of a base portion 15.

FIG. 16 is a diagram illustrating the motor 11 a. The motor 11 a is athree-phase motor. The motor 11 a includes a rotating portion 2 a, astationary portion 3 a, and a bearing mechanism 4 a. The rotatingportion 2 a includes a rotor magnet 22, a rotor holder 23, and ametallic yoke portion 24.

The rotor holder 23 includes a tubular portion 231 arrangedsubstantially in the shape of a cylinder and centered on a central axisJ1. The tubular portion 231 is arranged to extend downward from a lowersurface of the rotor holder 23. The yoke portion 24 includes a top plateportion 241 and a cylindrical portion 242. The top plate portion 241includes a cylindrical burring portion 241 a arranged to extenddownward. The rotor holder 23 is press fitted to the burring portion 241a, so that the yoke portion 24 and the rotor holder 23 are fixed to eachother. The rotor magnet 22 is fixed to an inner circumferential surfaceof the cylindrical portion 242. Referring to FIG. 15, the cylindricalportion 242 is fixed to an inner circumferential surface of a side wallportion 124 of a cup 121.

Referring to FIG. 16, the stationary portion 3 a includes a motor baseportion 34 and a stator 32. The motor base portion 34 is arranged on anupper surface of the support portion 16 as illustrated in FIG. 15. Thestator 32 is fixed to an outer circumferential surface of a cylindricalholder 341 arranged in a center of the motor base portion 34.

The bearing mechanism 4 a includes a shaft 41, a thrust plate 42, abearing portion 44 a, and a thrust cap 45. An upper portion of the shaft41 is fixed to a central hole portion of the rotor holder 23. The thrustplate 42 is fixed to a lower portion of the shaft 41.

The bearing portion 44 a includes a tubular sleeve 49 and a bearinghousing 40. The sleeve 49 is defined by a metallic sintered body. Alower portion of the bearing housing 40 is fixed inside the holder 341of the motor base portion 34. The tubular portion 231 is arrangedradially outward of the bearing housing 40. The bearing housing 40 isarranged to cover an outer circumferential surface of the sleeve 49. Thesleeve 49 is arranged to cover an outer circumference of the shaft 41.The thrust cap 45 is arranged to close a bottom portion of the bearinghousing 40. In a lower portion of the bearing mechanism 4 a, the sleeve49 is axially opposed to the thrust plate 42. In an upper portion of thebearing mechanism 4 a, each of the sleeve 49 and the bearing housing 40is axially opposed to the rotor holder 23.

Referring to FIG. 15, a lower end portion of the bearing portion 44 a,that is, a lower end portion of the bearing housing 40, is arranged at alevel higher than that of a lower end of an impeller 12, that is, alower end of the side wall portion 124 of the cup 121.

Referring to FIG. 17, a gap 57 is defined between an outer edge portionof the thrust plate 42 and a lower portion of an inner circumferentialsurface of the bearing housing 40, and between a lower surface of thethrust plate 42 and an upper surface of the thrust cap 45. Hereinafter,the gap 57 will be referred to as a “lower gap 57”. A lower surface 492of the sleeve 49, which faces downward in the axial direction, isarranged axially opposite an upper annular surface 422 of the thrustplate 42, and a gap 581 is defined between the lower surface 492 and theupper annular surface 422. Hereinafter, the gap 581 will be referred toas a “lower thrust gap 581”. A radial gap 51 is defined between an innercircumferential surface 491 of the sleeve 49 and an outercircumferential surface 411 of the shaft 41. A lower surface of therotor holder 23 includes an annular surface 232 facing downward in theaxial direction and arranged around the shaft 41 and inside of thetubular portion 231. The surface 232 is arranged axially opposite eachof an upper surface 493 of the sleeve 49 and an upper surface 401 of thebearing housing 40, each of which faces upward in the axial direction.Hereinafter, the surface 232 will be referred to as a “rotor annularsurface 232”. A gap 582 is defined between the rotor annular surface 232and each of the upper surface 493 of the sleeve 49 and the upper surface401 of the bearing housing 40. Hereinafter, the gap 582 will be referredto as an “upper thrust gap 582”. A gap 59 is defined between an upperportion of an outer circumferential surface 402 of the bearing housing40 and an inner circumferential surface of the tubular portion 231 ofthe rotor holder 23. The gap 59 is arranged to gradually increase inwidth with decreasing height. Hereinafter, the gap 59 will be referredto as a “seal gap 59”.

In the motor 11 a, the seal gap 59, the upper thrust gap 582, the radialgap 51, the lower thrust gap 581, and the lower gap 57 are arranged totogether define a single continuous bladder structure 5. A lubricatingoil 46 is arranged continuously in the bladder structure 5. A sealportion 59 a arranged to retain the lubricating oil 46 through capillaryaction is defined in the seal gap 59. A surface of the lubricating oil46 is defined only in the seal gap 59. In the following description, thethrust plate 42, which is arranged to extend radially outward from theshaft 41 at a bottom portion of the bladder structure 5, will bereferred to as a “first thrust portion 42”. The rotor holder 23, whichis arranged to extend radially outward from the upper portion of theshaft 41, will be referred to as a “second thrust portion 23”.

The lower surface 492 of the sleeve 49 includes a thrust dynamicpressure groove array similar to the thrust dynamic pressure groovearray 721 illustrated in FIG. 6 defined therein, and a lower thrustdynamic pressure bearing portion 693 arranged to generate a fluiddynamic pressure acting in a thrust direction is defined in the lowerthrust gap 581. The upper surface 401 of the bearing housing 40 includesa thrust dynamic pressure groove array similar to the thrust dynamicpressure groove array 722 illustrated in FIG. 7 defined therein, and anupper thrust dynamic pressure bearing portion 694 arranged to generate afluid dynamic pressure in the lubricating oil 46 is defined in the upperthrust gap 582. In other words, the upper surface 401 of the bearinghousing 40, which corresponds to an upward-facing thrust dynamicpressure bearing surface, and the rotor annular surface 232, whichcorresponds to a downward-facing thrust dynamic pressure bearingsurface, are arranged to together define the upper thrust dynamicpressure bearing portion 694. The rotating portion 2 a is axiallysupported by each of the lower and upper thrust dynamic pressure bearingportions 693 and 694. In addition, as in the first preferred embodiment,a radial dynamic pressure bearing portion 68 is defined in the radialgap 51, and the shaft 41 is thereby supported in the radial direction.

Referring to FIG. 18, an upper portion of the inner circumferentialsurface 491 of the sleeve 49 includes an inclined surface 494 arrangedto extend radially inward and obliquely downward from the upper surface493 of the sleeve 49. A portion of a radial dynamic pressure groovearray arranged to define the radial dynamic pressure bearing portion 68is defined in the inclined surface 494. When the shaft 41 is tiltedwhile the fan 1 a is driven, the inclined surface 494 extends along theouter circumferential surface 411 of the shaft 41 in a gap 56 definedbetween the inclined surface 494 and the outer circumferential surface411 of the shaft 41. A fluid dynamic pressure is thereby generated inthe gap 56, so that the shaft 41 is prevented from coming into contactwith an upper portion of the sleeve 49.

In the second preferred embodiment, as well as in the first preferredembodiment, use of a fluid dynamic bearing mechanism as the bearingmechanism contributes to reducing vibrations of the fan 1 a. Since thebearing mechanism 4 a has the full-fill structure, a leakage of thelubricating oil 46 due to a difference in pressure between seal portionsdoes not occur.

Because a lower end of the bearing portion 44 a is arranged at a levelhigher than that of the lower end of the impeller 12, a center ofgravity of the motor 11 a is located inside the impeller 12, and theimpeller 12 is capable of stable rotation. Because the motor 11 a is athree-phase motor, the motor 11 a is capable of causing the impeller 12to rotate in a sufficient manner even when the motor 11 a has arelatively small size. Also in the second preferred embodiment, theradial width of the radial gap 51 is arranged to be 5 μm or greater inorder to achieve a sufficient reduction in the vibrations of the fan 1a, and is arranged to be 20 μm or less in order to generate a sufficientfluid dynamic pressure in the radial gap 51. More preferably, the widthof the radial gap 51 is arranged in the range of about 5 μm to about 10μm. The same is true of other preferred embodiments of the presentinvention described below.

In addition, while the motor 11 a is stationary, a magnetic center ofthe stator 32 is located at a level lower than that of a magnetic centerof the rotor magnet 22. This contributes to reducing a force that actsto lift the impeller 12 relative to the stationary portion 3 a duringrotation of the fan 1 a. This contributes to reducing an increase in abearing loss that occurs in the lower thrust dynamic pressure bearingportion 693 in the case of the motor 11 a illustrated in FIG. 17.

FIG. 19 is a cross-sectional view of a motor 11 a according to amodification of the second preferred embodiment. A bearing mechanism 4 aof the motor 11 a includes a bearing portion 44 b defined by a singlesleeve made of a metal. The bearing mechanism 4 a does not include thefirst thrust portion 42. A lower end portion 412 of a shaft 41 isarranged to have a diameter slightly greater than that of a remainingportion of the shaft 41. The lower end portion 412 is arranged axiallyopposite a lower surface of the bearing portion 44 b. An annularmagnetic member 331 is arranged on an upper surface of a motor baseportion 34 and at a position axially opposed to a rotor magnet 22. Amagnetic action is generated between the magnetic member 331 and therotor magnet 22 to attract the rotor magnet 22 downward. The bearingmechanism 4 a according to the present modification of the secondpreferred embodiment is otherwise similar in structure to the bearingmechanism 4 a illustrated in FIG. 16.

The bearing portion 44 b includes a communicating hole 445 arranged toextend in the vertical direction through the bearing portion 44 b. Inthe bearing mechanism 4 a, an upper thrust dynamic pressure bearingportion 694 as a thrust dynamic pressure bearing portion is defined inan upper thrust gap 582 defined between a rotor annular surface 232 andan upper surface of the bearing portion 44 b. The communicating hole 445is arranged to connect the upper thrust gap 582 and a lower portion of aradial gap 51 with each other. While the motor 11 a is driven, alubricating oil 46 is arranged to circulate through the upper thrust gap582, the radial gap 51, and the communicating hole 445. A rotatingportion 2 a of the motor 11 a is stably supported in the thrustdirection with respect to a stationary portion 3 a thereof through thethrust dynamic pressure bearing portion 694 and the magnetic actiongenerated between the magnetic member 331 and the rotor magnet 22.

FIG. 20 is a cross-sectional view of a motor 11 a according to anothermodification of the second preferred embodiment. In the motor 11 a, alower thrust dynamic pressure bearing portion 695 is defined between anupper surface 451 of a thrust cap 45 and a downward-facing “lowerannular surface” 423 of a first thrust portion 42 as illustrated in FIG.16. The lower annular surface 423 is a surface of the first thrustportion 42 which faces downward in the axial direction. An upper thrustdynamic pressure bearing portion 694 is defined between a rotor annularsurface 232 of a second thrust portion 23 and an upper surface 401 of abearing housing 40. The upper surface 401 faces upward in the axialdirection. A rotating portion 2 a of the motor 11 a is stably supportedin the axial direction with respect to a stationary portion 3 a thereofthrough the lower and upper thrust dynamic pressure bearing portions 695and 694 and a magnetic action generated between a magnetic member 331and a rotor magnet 22.

FIG. 21 is a cross-sectional view of a motor 11 a according to yetanother modification of the second preferred embodiment. In the motor 11a, a first lower thrust dynamic pressure bearing portion 691 is definedin a first lower thrust gap 52 defined between an upper annular surface422 of a first thrust portion 42 and a lower surface 492 of a sleeve 49,which is axially opposed to the upper annular surface 422. A secondlower thrust dynamic pressure bearing portion 692 is defined in a secondlower thrust gap 53 defined between a lower annular surface 423 of thethrust plate 42 and an upper surface 451 of a thrust cap 45. The thrustplate 42 is supported in the axial direction through the first andsecond lower thrust dynamic pressure bearing portions 691 and 692.

FIG. 22 is a cross-sectional view of a motor 11 a according to yetanother modification of the second preferred embodiment. In the motor 11a, a bearing housing 40 a is defined by a single continuous member. Thebearing housing 40 a includes a substantially cylindrical side portion403 arranged to cover an outer circumferential surface of a sleeve 49,and a bottom portion 404 arranged to close a bottom portion of the sideportion 403. In FIG. 22, a lower thrust dynamic pressure bearing portion693 and an upper thrust dynamic pressure bearing portion 694 are definedin a lower thrust gap 581 and an upper thrust gap 582, respectively, asis the case with the bearing mechanism 4 a illustrated in FIG. 16.

Note that, as in FIG. 20, it may be so arranged that a lower thrustdynamic pressure bearing portion 695 is defined below a first thrustportion 42, while the upper thrust dynamic pressure bearing portion 694is defined below a second thrust portion 23. Also note that, as in FIG.21, a first lower thrust dynamic pressure bearing portion 691 and asecond lower thrust dynamic pressure bearing portion 692 may be definedabove and below, respectively, the first thrust portion 42.

Third Preferred Embodiment

FIG. 23 is a cross-sectional view of a centrifugal fan 1 b according toa third preferred embodiment of the present invention. Hereinafter, thecentrifugal fan will be referred to simply as the fan. The fan 1 bincludes a motor 11 b, an impeller 12 a, and a housing 13 a. In thefollowing description, those members or portions of the fan 1 b whichhave their equivalents in the first or second preferred embodiment aredenoted by the same reference numerals as those of their equivalents inthe first or second preferred embodiment. The housing 13 a includes abase portion 131, a side wall portion 132, and a cover portion 133. Thebase portion 131 is arranged to support the motor 11 b. The side wallportion 132 is arranged to surround an outer circumference of theimpeller 12 a. The cover portion 133 is arranged axially above aplurality of blades 122 of the impeller 12 a.

FIG. 24 is a diagram illustrating the motor 11 b. The motor 11 b is athree-phase outer-rotor motor. The motor 11 b includes a rotatingportion 2 b, a stationary portion 3 b, and a bearing mechanism 4 b. Therotating portion 2 b includes a rotor magnet 22 and a rotor holder 23 a.The rotating portion 2 b is supported through the bearing mechanism 4 bsuch that the rotating portion 2 b is rotatable about a central axis J1with respect to the stationary portion 3 b.

The rotor holder 23 a includes a top plate portion 241, a tubularportion 231, and a cylindrical portion 242. The top plate portion 241 isarranged substantially in the shape of a disk and centered on thecentral axis J1. Each of the tubular portion 231 and the cylindricalportion 242 is arranged substantially in the shape of a cylinder andcentered on the central axis J1. Each of the tubular portion 231 and thecylindrical portion 242 is arranged to extend downward from a lowersurface of the top plate portion 241. The top plate portion 241, thetubular portion 231, the cylindrical portion 242, and a shaft 41 a ofthe bearing mechanism 4 b, which will be described below, are defined bya single member. The tubular portion 231 is arranged radially outward ofthe shaft 41 a. The cylindrical portion 242 is arranged radially outwardof the tubular portion 231. The rotor magnet 22 is fixed to an innercircumferential surface of the cylindrical portion 242.

The stationary portion 3 b includes a substantially cylindrical bearingsupport portion 31, a stator 32, and a circuit board 33. A lower portionof the bearing support portion 31 is fixed to an inner circumferentialsurface of the base portion 131 which defines a central hole portion ofthe base portion 131. The stator 32 is fixed to an outer circumferentialsurface of the bearing support portion 31 on an upper side of the baseportion 131. The stator 32 is arranged radially inside the rotor magnet22. The circuit board 33 is fixed onto the base portion 131. The stator32 and the circuit board 33 are electrically connected with each other.While the motor 11 b is driven, a turning force is generated between therotor magnet 22 and the stator 32.

While the motor 11 b is stationary, a magnetic center of the stator 32is located at a level lower than that of a magnetic center of the rotormagnet 22. This contributes to reducing a force that acts to lift theimpeller 12 a relative to the stationary portion 3 b during rotation ofthe fan 1 b. The same is true of other preferred embodiments of thepresent invention described below.

An annular magnetic member 331 is arranged on the base portion 131. Themagnetic member 331 is arranged under the rotor magnet 22. In the fan 1b, magnetic attraction forces that act to attract the rotor magnet 22downward are generated between the rotor magnet 22 and the stator 32,and between the rotor magnet 22 and the magnetic member 331. Thiscontributes to further reducing the force that acts to lift the impeller12 a relative to the stationary portion 3 b during the rotation of thefan 1 b. The same is true of other preferred embodiments of the presentinvention described below.

The bearing mechanism 4 b includes the shaft 41 a, a thrust plate 42, abearing portion 44 a, a thrust cap 45, which corresponds to a capmember, and a lubricating oil 46. The shaft 41 a is arranged to extenddownward from the lower surface of the top plate portion 241 of therotor holder 23 a. The shaft 41 a is arranged substantially in the shapeof a cylinder and centered on the central axis J1. The thrust plate 42is fixed to a bottom portion of the shaft 41 a. The thrust plate 42 isarranged to extend radially outward from a lower end of the shaft 41 a.The thrust plate 42 corresponds to a thrust portion arranged axiallyopposite the bearing portion 44 a.

The bearing portion 44 a is arranged radially inward of the stator 32.The bearing portion 44 a includes a tubular sleeve 49 and a bearinghousing 40. The sleeve 49 is defined by a metallic sintered body. Alower portion of the bearing housing 40 is fixed inside the bearingsupport portion 31. The tubular portion 231 is arranged radially outwardof the bearing housing 40. The bearing housing 40 is arranged to coveran outer circumferential surface of the sleeve 49. The sleeve 49 isarranged to cover an outer circumference of the shaft 41 a. The thrustcap 45 is arranged to close a bottom portion of the bearing housing 40.In a lower portion of the bearing mechanism 4 b, the sleeve 49 isaxially opposed to the thrust plate 42. In an upper portion of thebearing mechanism 4 b, each of the sleeve 49 and the bearing housing 40is axially opposed to the top plate portion 241 of the rotor holder 23a.

Referring to FIG. 25, a lower gap 57 is defined between an outer edgeportion of the thrust plate 42 and a lower portion of an innercircumferential surface of the bearing housing 40, and between a lowersurface of the thrust plate 42 and an upper surface of the thrust cap45. A lower surface 492 of the sleeve 49, which faces downward in theaxial direction, is arranged axially opposite an upper annular surface422 of the thrust plate 42, and a lower thrust gap 581 is definedbetween the lower surface 492 and the upper annular surface 422. Aradial gap 51 is defined between an inner circumferential surface 491 ofthe sleeve 49 and an outer circumferential surface 411 of the shaft 41a. A lower surface of the rotor holder 23 a includes an annular “rotorannular surface” 232 facing downward in the axial direction and arrangedaround the shaft 41 a and inside of the tubular portion 231. The rotorannular surface 232 is arranged axially opposite each of an uppersurface 493 of the sleeve 49 and an upper surface 401 of the bearinghousing 40, each of which faces upward in the axial direction. An upperthrust gap 582 is defined between the rotor annular surface 232 and eachof the upper surface 493 of the sleeve 49 and the upper surface 401 ofthe bearing housing 40. A seal gap 59 is defined between an upperportion of an outer circumferential surface 402 of the bearing housing40 and an inner circumferential surface of the tubular portion 231 ofthe rotor holder 23 a. The seal gap 59 is arranged to gradually increasein width with decreasing height.

In the motor 11 b, the seal gap 59, the upper thrust gap 582, the radialgap 51, the lower thrust gap 581, and the lower gap 57 are arranged totogether define a single continuous bladder structure 5. The lubricatingoil 46 is arranged continuously in the bladder structure 5. A sealportion 59 a arranged to retain the lubricating oil 46 through capillaryaction is defined in the seal gap 59. A surface of the lubricating oil46 is defined only in the seal gap 59.

The lower surface 492 of the sleeve 49 includes a thrust dynamicpressure groove array similar to the thrust dynamic pressure groovearray 721 illustrated in FIG. 6 defined therein, and a lower thrustdynamic pressure bearing portion 693 arranged to generate a fluiddynamic pressure acting in the thrust direction is defined in the lowerthrust gap 581. The upper surface 493 of the sleeve 49 includes a thrustdynamic pressure groove array similar to the thrust dynamic pressuregroove array 722 illustrated in FIG. 7 defined therein, and an upperthrust dynamic pressure bearing portion 694 arranged to generate a fluiddynamic pressure in the lubricating oil 46 is defined in the upperthrust gap 582. The rotating portion 2 b is axially supported by each ofthe lower and upper thrust dynamic pressure bearing portions 693 and694. In addition, as in the first preferred embodiment, a radial dynamicpressure bearing portion 68 is defined in the radial gap 51, and theshaft 41 a is thereby supported in the radial direction. Note that anupper portion of the inner circumferential surface 491 of the sleeve 49may include an inclined surface similar to the inclined surface 494illustrated in FIG. 18.

In the third preferred embodiment, as well as in the first preferredembodiment, use of a fluid dynamic bearing mechanism as the bearingmechanism contributes to reducing vibrations of the fan 1 b. Since thebearing mechanism 4 b has the full-fill structure, a leakage of thelubricating oil 46 due to a difference in pressure between seal portionsdoes not occur. The same is true of other preferred embodiments of thepresent invention described below.

The impeller 12 a illustrated in FIG. 23 is made of a resin, andincludes a substantially cylindrical fixing portion 124 a, the pluralityof blades 122, and a plurality of blade support portions 126. The fixingportion 124 a is fixed to an outer circumferential surface of thecylindrical portion 242 of the rotor holder 23 a. The fixing portion 124a defines a portion of the rotating portion 2 b of the motor 11 b. Ifeach of the top plate portion 241 and the cylindrical portion 242 of therotor holder 23 a is regarded as a portion of the impeller 12 a, the topplate portion 241 defines a top face portion of a cup arrangedsubstantially in the shape of a covered cylinder. The top face portionis arranged to extend perpendicularly to the central axis J1. Inaddition, a structure made up of the cylindrical portion 242 and thefixing portion 124 a defines a side wall portion of the cup. The sidewall portion is arranged to extend downward from an outer edge portionof the top plate portion 241.

The blade support portions 126 are arranged to extend radially outwardfrom an outer circumferential surface of the fixing portion 124 a withthe central axis J1 as a center. Each of the blades 122 is supported onan end of a separate one of the blade support portions 126. The blades122 are arranged to extend radially outward from the ends of the bladesupport portions 126 with the central axis J1 as a center. The fixingportion 124 a, the plurality of blade support portions 126, and theplurality of blades 122 are defined integrally with one another by aresin injection molding process.

The fan 1 b is arranged to produce air currents traveling from an upperopening toward a side of the fan 1 b through rotation of the impeller 12a about the central axis J1 caused by the motor 11 b.

An upper end of each blade 122 is arranged at a level lower than that ofthe lower surface of the top plate portion 241 of the rotor holder 23 a.The lower surface of the top plate portion 241 corresponds to adownward-facing thrust dynamic pressure bearing surface of the upperthrust dynamic pressure bearing portion 694. A center of gravity of theimpeller 12 a is thereby located on an axially lower side. This enablesthe impeller 12 a to rotate stably. As a result, a reduction in thevibrations of the fan 1 b is achieved. Furthermore, a lower end of thecover portion 133 of the housing 13 a is also arranged at a level lowerthan that of the lower surface of the top plate portion 241 of the rotorholder 23 a. The blades 122 are thereby located further downward in theaxial direction, and the center of gravity of the impeller 12 a is alsothereby located further downward in the axial direction. As a result, anadditional reduction in the vibrations of the fan 1 b is achieved.

The upper end of each of the blades 122 is arranged at a level lowerthan that of a center of pressure of an upper radial dynamic pressurebearing portion 681. The center of pressure of the upper radial dynamicpressure bearing portion 681 refers to an axial center of a pressuredistribution of the upper radial dynamic pressure bearing portion 681while the rotating portion 2 b is rotated. As a result of the abovearrangement, the center of gravity of the impeller 12 a is located onthe axially lower side. As a result, a reduction in the vibrations ofthe fan 1 b is achieved. Instead of the above arrangement, the upper endof each of the blades 122 may be arranged at a level lower than that ofa center of the upper radial dynamic pressure bearing portion 681. Thecenter of the upper radial dynamic pressure bearing portion 681 refersto an axial center of a region extending from an axially upper end to anaxially lower end of a first radial dynamic pressure groove array 711(see FIG. 5). This arrangement also causes the center of gravity of theimpeller 12 a to be located on the axially lower side. As a result, areduction in the vibrations of the fan 1 b is achieved.

In the fan 1 b, an upper surface of the top plate portion 241 of therotor holder 23 a may include a hole portion defined therein, and aweight similar to the weight 129 illustrated in FIG. 1 may be arrangedin this hole portion. A weight may also be arranged on a lower end ofthe cylindrical portion 242 of the rotor holder 23 a or on a lower endof the fixing portion 124 a of the impeller 12 a. Arrangement of theseweights can reduce unbalance of each of the impeller 12 a and therotating portion 2 b of the motor 11 b. The reduction in the unbalanceleads to a reduction in vibrations of the fan 1 b owing to adisplacement of the center of gravity of any of the impeller 12 a andthe motor 11 b from the central axis J1. Moreover, when the radialdynamic pressure bearing portion 68 is arranged axially between the twoweights, each of the rotating portion 2 b and the impeller 12 a iscapable of stable rotation, and a further reduction in the vibrations isachieved. The same is true of other preferred embodiments of the presentinvention described below.

FIG. 26 is a diagram illustrating a fan 1 c according to a modificationof the third preferred embodiment. The fan 1 c is different from the fan1 b illustrated in FIG. 23 in the shape of a housing 13 a and the shapeof an impeller 12 a. Referring to FIG. 26, an upper end of each of aplurality of blades 122 is arranged at a level lower than that of alower surface of a top plate portion 241 of a rotor holder 23 a. Acenter of gravity of the impeller 12 a is thereby located on an axiallylower side. As a result, similarly to the fan 1 b, the fan 1 c is ableto achieve reduced vibration. A lower end of a cover portion 133 of thehousing 13 a is also arranged at a level lower than that of the lowersurface of the top plate portion 241 of the rotor holder 23 a. Thecenter of gravity of the impeller 12 a is thereby located furtherdownward in the axial direction. As a result, an additional reduction invibrations of the fan 1 c is achieved.

The upper end of each of the blades 122 is arranged at a level lowerthan that of a center of pressure of an upper radial dynamic pressurebearing portion 681. The center of gravity of the impeller 12 a isthereby located on the axially lower side. As a result, a reduction inthe vibrations of the fan 1 c is achieved. Instead of the abovearrangement, the upper end of each of the blades 122 may be arranged ata level lower than that of a center of the upper radial dynamic pressurebearing portion 681. This arrangement also causes the center of gravityof the impeller 12 a to be located on the axially lower side. As aresult, a reduction in the vibrations of the fan 1 c is achieved.

A lower end of each of the blades 122 is arranged at a level higher thanthat of an upper annular surface 422 of a thrust plate 42. The upperannular surface 422 corresponds to an upward-facing thrust dynamicpressure bearing surface of a lower thrust dynamic pressure bearingportion 693. The center of gravity of the impeller 12 a is therebylocated between an upper end and a lower end of a shaft 41 a. As aresult, the impeller 12 a is capable of stable rotation, and a reductionin the vibrations of the fan 1 c is achieved.

FIG. 27 is a diagram illustrating a fan 1 d according to anothermodification of the third preferred embodiment. The fan 1 d is differentfrom the fan 1 b illustrated in FIG. 23 in the shape of a housing 13 aand the shape of an impeller 12 a. Referring to FIG. 27, a lower end ofeach of a plurality of blades 122 is arranged at a level higher thanthat of an upper annular surface 422 of a thrust plate 42. A center ofgravity of the impeller 12 a is thereby located between an upper end anda lower end of a shaft 41 a. As a result, a reduction in vibrations ofthe fan 1 d is achieved.

While preferred embodiments of the present invention have been describedabove, it will be understood that the present invention is not limitedto the above-described preferred embodiments, and that a variety ofmodifications are possible.

In the second preferred embodiment, the thrust dynamic pressure groovearray may be defined in the upper surface 493 of the sleeve 49 so thatthe thrust dynamic pressure bearing portion may be defined between theupper surface 493 of the sleeve 49 and the lower surface of the secondthrust portion 23. In the third preferred embodiment, the thrust dynamicpressure groove array may be defined in the upper surface 401 of thebearing housing 40 so that the thrust dynamic pressure bearing portionmay be defined between the upper surface 401 of the bearing housing 40and the lower surface of the rotor holder 23 a.

In the first preferred embodiment, an upper portion of the first radialdynamic pressure groove array 711 may be defined in the second inclinedsurface 441 b. Also, no dynamic pressure grooves may be defined in thesecond inclined surface 441 b of the bearing portion 44. Even in thiscase, provision of the second inclined surface 441 b secures an area tosupport the shaft 41 so that bearing rigidity can be improved to acertain extent. The same is true of the sleeve 49 of each of the fans 1a and 1 b according to the second and third preferred embodiments,respectively.

In each of the above-described preferred embodiments, each of the firstand second radial dynamic pressure groove arrays 711 and 712 may bedefined in the outer circumferential surface 411 of the shaft 41. Also,the thrust dynamic pressure groove arrays 721 and 722 may be defined inthe upper surface and the lower surface, respectively, of the firstthrust portion (i.e., the thrust plate) 42. Also, the communicating hole421 a may not necessarily be provided in the bearing mechanism 4.

In the first preferred embodiment, the outer circumferential surface 411of the shaft 41 may be arranged to include a portion which has adecreased diameter in the vicinity of a top portion of the bearingportion 44 so that the seal portion may be defined between this portionand the inner circumferential surface 441 of the bearing portion 44.Also, the upper portion of the shaft 41 may be directly fixed to theimpeller 12. Also, the shaft 41 may be fixed to the impeller 12 throughtwo or more members. Also, a viscoseal that generates a fluid dynamicpressure through a dynamic pressure groove defined in the seal gap maybe used as the seal portion. The same is true of each of the second andthird preferred embodiments.

In the first preferred embodiment, a metallic member may be arranged, asthe weight, in the balance correction portion 125 of the top faceportion 123 of the impeller 12. Also, the balance correction portion 125may be defined by a through hole or a cut. The same is true of thebalance correction portion 124 a of the side wall portion 124. Also, theweight may be arranged on only one of the top face portion 123 and thelower end portion 124 a of the side wall portion 124. Also, theunbalance of the rotating portion 2 may be eliminated by removing aportion of the top face portion 123 or a portion of the side wallportion 124. The same is true of each of the second and third preferredembodiments.

The magnetic center of the stator 32 and the magnetic center of therotor magnet 22 may be arranged to coincide with each other in the axialdirection when the motor 11, 11 a, 11 b, 11 c, or 11 d is stationary. Areduction in the vibrations of the motor 11, 11 a, lib, 11 c, or 11 dcan thereby be achieved.

Each of the motors 11 and 11 a may be used as a motor of a fan ofanother type, such as a centrifugal fan. Each of the motors 11 b to 11 dmay be used as a motor of a fan of another type, such as an axial fan. Afan in which any of the motors 11 and 11 a to 11 d is used is optimalfor use with a device having a hard disk installed therein, such as aserver. In the server, the fan is disposed at a position close to thehard disk. Therefore, if the fan is of a type which generatessignificant vibrations, read or write errors tend to easily occur in thehard disk. In contrast, read or write errors do not easily occur in thehard disk if the fan installed in the server uses any of the motors 11and 11 a to 11 d.

Features of the above-described preferred embodiments and themodifications thereof may be combined appropriately as long as noconflict arises.

The present invention is applicable to fans arranged to produce aircurrents.

1. A fan comprising: a motor; and an impeller including a plurality ofblades, and arranged to rotate about a central axis through the motor toproduce air currents; wherein the motor includes: a stationary portion;and a rotating portion rotatably supported by the stationary portion;the stationary portion includes: a stator; and a bearing portionarranged inside of the stator; the rotating portion includes: a rotormagnet arranged radially outside the stator; a shaft inserted in thebearing portion, and having an upper portion fixed to the impellerdirectly or through one or more members; and a thrust portion arrangedaxially opposite the bearing portion, and including an annular surfacearranged around the shaft; a radial dynamic pressure bearing portionarranged to generate a fluid dynamic pressure in a lubricating oil isdefined in a radial gap defined between an inner circumferential surfaceof the bearing portion and an outer circumferential surface of theshaft, while a thrust dynamic pressure bearing portion arranged togenerate a fluid dynamic pressure in the lubricating oil is defined in athrust gap defined between the annular surface and a surface of thebearing portion which is axially opposed to the annular surface; asingle seal gap arranged in an annular shape and centered on the centralaxis is defined between the stationary and rotating portions; and theseal gap, the radial gap, and the thrust gap are arranged to togetherdefine a single continuous bladder structure, the lubricating oil isarranged continuously in the bladder structure, and a surface of thelubricating oil is defined only in the seal gap.
 2. The fan according toclaim 1, wherein the bearing portion includes: a tubular sleeve; and abearing housing arranged to cover an outer circumferential surface ofthe sleeve.
 3. The fan according to claim 2, wherein the stationaryportion further includes a cap member arranged to close a lower end ofthe bearing housing.
 4. The fan according to claim 2, wherein thebearing housing is defined by a single continuous member; and thebearing housing includes: a substantially cylindrical side portionarranged to cover the outer circumferential surface of the sleeve; and abottom portion arranged to close a bottom portion of the side portion.5. The fan according to claim 1, wherein the thrust portion is a thrustplate arranged to extend radially outward from the shaft at a bottomportion of the bladder structure; an upper surface of the thrust plateincludes an upward-facing thrust dynamic pressure bearing surfacedefined by the annular surface; the bearing portion includes adownward-facing thrust dynamic pressure bearing surface arranged to facedownward in an axial direction; the upward-facing and downward-facingthrust dynamic pressure bearing surfaces are arranged axially oppositeeach other; and the thrust dynamic pressure bearing portion is definedby the upward-facing and downward-facing thrust dynamic pressure bearingsurfaces.
 6. The fan according to claim 2, wherein the thrust portion isa thrust plate arranged to extend radially outward from the shaft at abottom portion of the bladder structure; an upper surface of the thrustplate includes an upward-facing thrust dynamic pressure bearing surfacedefined by the annular surface; the bearing portion includes adownward-facing thrust dynamic pressure bearing surface arranged to facedownward in an axial direction; the upward-facing and downward-facingthrust dynamic pressure bearing surfaces are arranged axially oppositeeach other; and the thrust dynamic pressure bearing portion is definedby the upward-facing and downward-facing thrust dynamic pressure bearingsurfaces.
 7. The fan according to claim 3, wherein the thrust portion isa thrust plate arranged to extend radially outward from the shaft at abottom portion of the bladder structure; an upper surface of the thrustplate includes an upward-facing thrust dynamic pressure bearing surfacedefined by the annular surface; the bearing portion includes adownward-facing thrust dynamic pressure bearing surface arranged to facedownward in an axial direction; the upward-facing and downward-facingthrust dynamic pressure bearing surfaces are arranged axially oppositeeach other; and the thrust dynamic pressure bearing portion is definedby the upward-facing and downward-facing thrust dynamic pressure bearingsurfaces.
 8. The fan according to claim 4, wherein the thrust portion isa thrust plate arranged to extend radially outward from the shaft at abottom portion of the bladder structure; an upper surface of the thrustplate includes an upward-facing thrust dynamic pressure bearing surfacedefined by the annular surface; the bearing portion includes adownward-facing thrust dynamic pressure bearing surface arranged to facedownward in an axial direction; the upward-facing and downward-facingthrust dynamic pressure bearing surfaces are arranged axially oppositeeach other; and the thrust dynamic pressure bearing portion is definedby the upward-facing and downward-facing thrust dynamic pressure bearingsurfaces.
 9. The fan according to claim 5, wherein a lower end of eachof the blades is arranged at a level higher than that of theupward-facing thrust dynamic pressure bearing surface.
 10. The fanaccording to claim 6, wherein a lower end of each of the blades isarranged at a level higher than that of the upward-facing thrust dynamicpressure bearing surface.
 11. The fan according to claim 7, wherein alower end of each of the blades is arranged at a level higher than thatof the upward-facing thrust dynamic pressure bearing surface.
 12. Thefan according to claim 8, wherein a lower end of each of the blades isarranged at a level higher than that of the upward-facing thrust dynamicpressure bearing surface.
 13. The fan according to claim 5, wherein alower surface of the thrust plate includes another annular surface; andthe other annular surface is opposed to a bottom surface of the bladderstructure to define another thrust dynamic pressure bearing portion. 14.The fan according to claim 6, wherein a lower surface of the thrustplate includes another annular surface; and the other annular surface isopposed to a bottom surface of the bladder structure to define anotherthrust dynamic pressure bearing portion.
 15. The fan according to claim7, wherein a lower surface of the thrust plate includes another annularsurface; and the other annular surface is opposed to a bottom surface ofthe bladder structure to define another thrust dynamic pressure bearingportion.
 16. The fan according to claim 8, wherein a lower surface ofthe thrust plate includes another annular surface; and the other annularsurface is opposed to a bottom surface of the bladder structure todefine another thrust dynamic pressure bearing portion.
 17. The fanaccording to claim 9, wherein a lower surface of the thrust plateincludes another annular surface; and the other annular surface isopposed to a bottom surface of the bladder structure to define anotherthrust dynamic pressure bearing portion.
 18. The fan according to claim10, wherein a lower surface of the thrust plate includes another annularsurface; and the other annular surface is opposed to a bottom surface ofthe bladder structure to define another thrust dynamic pressure bearingportion.
 19. The fan according to claim 11, wherein a lower surface ofthe thrust plate includes another annular surface; and the other annularsurface is opposed to a bottom surface of the bladder structure todefine another thrust dynamic pressure bearing portion.
 20. The fanaccording to claim 12, wherein a lower surface of the thrust plateincludes another annular surface; and the other annular surface isopposed to a bottom surface of the bladder structure to define anotherthrust dynamic pressure bearing portion.
 21. The fan according to claim5, wherein the rotating portion includes a tubular portion arranged toextend downward and centered on the central axis, and arranged radiallyopposite an outer circumferential surface of the bearing portion; andthe seal gap is defined between an upper portion of the outercircumferential surface of the bearing portion and an innercircumferential surface of the tubular portion, the seal gap beingarranged to gradually increase in radial width with decreasing height.22. The fan according to claim 6, wherein the rotating portion includesa tubular portion arranged to extend downward and centered on thecentral axis, and arranged radially opposite an outer circumferentialsurface of the bearing portion; and the seal gap is defined between anupper portion of the outer circumferential surface of the bearingportion and an inner circumferential surface of the tubular portion, theseal gap being arranged to gradually increase in radial width withdecreasing height.
 23. The fan according to claim 7, wherein therotating portion includes a tubular portion arranged to extend downwardand centered on the central axis, and arranged radially opposite anouter circumferential surface of the bearing portion; and the seal gapis defined between an upper portion of the outer circumferential surfaceof the bearing portion and an inner circumferential surface of thetubular portion, the seal gap being arranged to gradually increase inradial width with decreasing height.
 24. The fan according to claim 8,wherein the rotating portion includes a tubular portion arranged toextend downward and centered on the central axis, and arranged radiallyopposite an outer circumferential surface of the bearing portion; andthe seal gap is defined between an upper portion of the outercircumferential surface of the bearing portion and an innercircumferential surface of the tubular portion, the seal gap beingarranged to gradually increase in radial width with decreasing height.25. The fan according to claim 9, wherein the rotating portion includesa tubular portion arranged to extend downward and centered on thecentral axis, and arranged radially opposite an outer circumferentialsurface of the bearing portion; and the seal gap is defined between anupper portion of the outer circumferential surface of the bearingportion and an inner circumferential surface of the tubular portion, theseal gap being arranged to gradually increase in radial width withdecreasing height.
 26. The fan according to claim 10, wherein therotating portion includes a tubular portion arranged to extend downwardand centered on the central axis, and arranged radially opposite anouter circumferential surface of the bearing portion; and the seal gapis defined between an upper portion of the outer circumferential surfaceof the bearing portion and an inner circumferential surface of thetubular portion, the seal gap being arranged to gradually increase inradial width with decreasing height.
 27. The fan according to claim 11,wherein the rotating portion includes a tubular portion arranged toextend downward and centered on the central axis, and arranged radiallyopposite an outer circumferential surface of the bearing portion; andthe seal gap is defined between an upper portion of the outercircumferential surface of the bearing portion and an innercircumferential surface of the tubular portion, the seal gap beingarranged to gradually increase in radial width with decreasing height.28. The fan according to claim 12, wherein the rotating portion includesa tubular portion arranged to extend downward and centered on thecentral axis, and arranged radially opposite an outer circumferentialsurface of the bearing portion; and the seal gap is defined between anupper portion of the outer circumferential surface of the bearingportion and an inner circumferential surface of the tubular portion, theseal gap being arranged to gradually increase in radial width withdecreasing height.
 29. The fan according to claim 5, wherein therotating portion further includes another thrust portion arranged toextend radially outward from the upper portion of the shaft; the bearingportion includes a surface arranged to face upward in the axialdirection; the other thrust portion includes another annular surfacearranged axially opposite the surface arranged to face upward in theaxial direction; and the surface arranged to face upward in the axialdirection and the other annular surface are arranged to together defineanother thrust dynamic pressure bearing portion.
 30. The fan accordingto claim 6, wherein the rotating portion further includes another thrustportion arranged to extend radially outward from the upper portion ofthe shaft; the bearing portion includes a surface arranged to faceupward in the axial direction; the other thrust portion includes anotherannular surface arranged axially opposite the surface arranged to faceupward in the axial direction; and the surface arranged to face upwardin the axial direction and the other annular surface are arranged totogether define another thrust dynamic pressure bearing portion.
 31. Thefan according to claim 7, wherein the rotating portion further includesanother thrust portion arranged to extend radially outward from theupper portion of the shaft; the bearing portion includes a surfacearranged to face upward in the axial direction; the other thrust portionincludes another annular surface arranged axially opposite the surfacearranged to face upward in the axial direction; and the surface arrangedto face upward in the axial direction and the other annular surface arearranged to together define another thrust dynamic pressure bearingportion.
 32. The fan according to claim 8, wherein the rotating portionfurther includes another thrust portion arranged to extend radiallyoutward from the upper portion of the shaft; the bearing portionincludes a surface arranged to face upward in the axial direction; theother thrust portion includes another annular surface arranged axiallyopposite the surface arranged to face upward in the axial direction; andthe surface arranged to face upward in the axial direction and the otherannular surface are arranged to together define another thrust dynamicpressure bearing portion.
 33. The fan according to claim 9, wherein therotating portion further includes another thrust portion arranged toextend radially outward from the upper portion of the shaft; the bearingportion includes a surface arranged to face upward in the axialdirection; the other thrust portion includes another annular surfacearranged axially opposite the surface arranged to face upward in theaxial direction; and the surface arranged to face upward in the axialdirection and the other annular surface are arranged to together defineanother thrust dynamic pressure bearing portion.
 34. The fan accordingto claim 10, wherein the rotating portion further includes anotherthrust portion arranged to extend radially outward from the upperportion of the shaft; the bearing portion includes a surface arranged toface upward in the axial direction; the other thrust portion includesanother annular surface arranged axially opposite the surface arrangedto face upward in the axial direction; and the surface arranged to faceupward in the axial direction and the other annular surface are arrangedto together define another thrust dynamic pressure bearing portion. 35.The fan according to claim 11, wherein the rotating portion furtherincludes another thrust portion arranged to extend radially outward fromthe upper portion of the shaft; the bearing portion includes a surfacearranged to face upward in the axial direction; the other thrust portionincludes another annular surface arranged axially opposite the surfacearranged to face upward in the axial direction; and the surface arrangedto face upward in the axial direction and the other annular surface arearranged to together define another thrust dynamic pressure bearingportion.
 36. The fan according to claim 12, wherein the rotating portionfurther includes another thrust portion arranged to extend radiallyoutward from the upper portion of the shaft; the bearing portionincludes a surface arranged to face upward in the axial direction; theother thrust portion includes another annular surface arranged axiallyopposite the surface arranged to face upward in the axial direction; andthe surface arranged to face upward in the axial direction and the otherannular surface are arranged to together define another thrust dynamicpressure bearing portion.
 37. The fan according to claim 29, wherein anupper end of each of the blades is arranged at a level lower than thatof the other annular surface.
 38. The fan according to claim 30, whereinan upper end of each of the blades is arranged at a level lower thanthat of the other annular surface.
 39. The fan according to claim 31,wherein an upper end of each of the blades is arranged at a level lowerthan that of the other annular surface.
 40. The fan according to claim32, wherein an upper end of each of the blades is arranged at a levellower than that of the other annular surface.
 41. The fan according toclaim 33, wherein an upper end of each of the blades is arranged at alevel lower than that of the other annular surface.
 42. The fanaccording to claim 34, wherein an upper end of each of the blades isarranged at a level lower than that of the other annular surface. 43.The fan according to claim 35, wherein an upper end of each of theblades is arranged at a level lower than that of the other annularsurface.
 44. The fan according to claim 36, wherein an upper end of eachof the blades is arranged at a level lower than that of the otherannular surface.
 45. The fan according to claim 37, further comprising acover portion arranged axially above the blades, wherein a lower end ofthe cover portion is arranged at a level lower than that of the otherannular surface.
 46. The fan according to claim 38, further comprising acover portion arranged axially above the blades, wherein a lower end ofthe cover portion is arranged at a level lower than that of the otherannular surface.
 47. The fan according to claim 39, further comprising acover portion arranged axially above the blades, wherein a lower end ofthe cover portion is arranged at a level lower than that of the otherannular surface.
 48. The fan according to claim 40, further comprising acover portion arranged axially above the blades, wherein a lower end ofthe cover portion is arranged at a level lower than that of the otherannular surface.
 49. The fan according to claim 41, further comprising acover portion arranged axially above the blades, wherein a lower end ofthe cover portion is arranged at a level lower than that of the otherannular surface.
 50. The fan according to claim 42, further comprising acover portion arranged axially above the blades, wherein a lower end ofthe cover portion is arranged at a level lower than that of the otherannular surface.
 51. The fan according to claim 43, further comprising acover portion arranged axially above the blades, wherein a lower end ofthe cover portion is arranged at a level lower than that of the otherannular surface.
 52. The fan according to claim 44, further comprising acover portion arranged axially above the blades, wherein a lower end ofthe cover portion is arranged at a level lower than that of the otherannular surface.
 53. The fan according to claim 29, wherein the rotatingportion includes a tubular portion arranged to extend downward andcentered on the central axis, and arranged radially opposite an outercircumferential surface of the bearing portion; and the seal gap isdefined between an upper portion of the outer circumferential surface ofthe bearing portion and an inner circumferential surface of the tubularportion, the seal gap being arranged to gradually increase in radialwidth with decreasing height.
 54. The fan according to claim 30, whereinthe rotating portion includes a tubular portion arranged to extenddownward and centered on the central axis, and arranged radiallyopposite an outer circumferential surface of the bearing portion; andthe seal gap is defined between an upper portion of the outercircumferential surface of the bearing portion and an innercircumferential surface of the tubular portion, the seal gap beingarranged to gradually increase in radial width with decreasing height.55. The fan according to claim 31, wherein the rotating portion includesa tubular portion arranged to extend downward and centered on thecentral axis, and arranged radially opposite an outer circumferentialsurface of the bearing portion; and the seal gap is defined between anupper portion of the outer circumferential surface of the bearingportion and an inner circumferential surface of the tubular portion, theseal gap being arranged to gradually increase in radial width withdecreasing height.
 56. The fan according to claim 32, wherein therotating portion includes a tubular portion arranged to extend downwardand centered on the central axis, and arranged radially opposite anouter circumferential surface of the bearing portion; and the seal gapis defined between an upper portion of the outer circumferential surfaceof the bearing portion and an inner circumferential surface of thetubular portion, the seal gap being arranged to gradually increase inradial width with decreasing height.
 57. The fan according to claim 33,wherein the rotating portion includes a tubular portion arranged toextend downward and centered on the central axis, and arranged radiallyopposite an outer circumferential surface of the bearing portion; andthe seal gap is defined between an upper portion of the outercircumferential surface of the bearing portion and an innercircumferential surface of the tubular portion, the seal gap beingarranged to gradually increase in radial width with decreasing height.58. The fan according to claim 34, wherein the rotating portion includesa tubular portion arranged to extend downward and centered on thecentral axis, and arranged radially opposite an outer circumferentialsurface of the bearing portion; and the seal gap is defined between anupper portion of the outer circumferential surface of the bearingportion and an inner circumferential surface of the tubular portion, theseal gap being arranged to gradually increase in radial width withdecreasing height.
 59. The fan according to claim 35, wherein therotating portion includes a tubular portion arranged to extend downwardand centered on the central axis, and arranged radially opposite anouter circumferential surface of the bearing portion; and the seal gapis defined between an upper portion of the outer circumferential surfaceof the bearing portion and an inner circumferential surface of thetubular portion, the seal gap being arranged to gradually increase inradial width with decreasing height.
 60. The fan according to claim 36,wherein the rotating portion includes a tubular portion arranged toextend downward and centered on the central axis, and arranged radiallyopposite an outer circumferential surface of the bearing portion; andthe seal gap is defined between an upper portion of the outercircumferential surface of the bearing portion and an innercircumferential surface of the tubular portion, the seal gap beingarranged to gradually increase in radial width with decreasing height.61. The fan according to claim 37, wherein the rotating portion includesa tubular portion arranged to extend downward and centered on thecentral axis, and arranged radially opposite an outer circumferentialsurface of the bearing portion; and the seal gap is defined between anupper portion of the outer circumferential surface of the bearingportion and an inner circumferential surface of the tubular portion, theseal gap being arranged to gradually increase in radial width withdecreasing height.
 62. The fan according to claim 38, wherein therotating portion includes a tubular portion arranged to extend downwardand centered on the central axis, and arranged radially opposite anouter circumferential surface of the bearing portion; and the seal gapis defined between an upper portion of the outer circumferential surfaceof the bearing portion and an inner circumferential surface of thetubular portion, the seal gap being arranged to gradually increase inradial width with decreasing height.
 63. The fan according to claim 39,wherein the rotating portion includes a tubular portion arranged toextend downward and centered on the central axis, and arranged radiallyopposite an outer circumferential surface of the bearing portion; andthe seal gap is defined between an upper portion of the outercircumferential surface of the bearing portion and an innercircumferential surface of the tubular portion, the seal gap beingarranged to gradually increase in radial width with decreasing height.64. The fan according to claim 40, wherein the rotating portion includesa tubular portion arranged to extend downward and centered on thecentral axis, and arranged radially opposite an outer circumferentialsurface of the bearing portion; and the seal gap is defined between anupper portion of the outer circumferential surface of the bearingportion and an inner circumferential surface of the tubular portion, theseal gap being arranged to gradually increase in radial width withdecreasing height.
 65. The fan according to claim 41, wherein therotating portion includes a tubular portion arranged to extend downwardand centered on the central axis, and arranged radially opposite anouter circumferential surface of the bearing portion; and the seal gapis defined between an upper portion of the outer circumferential surfaceof the bearing portion and an inner circumferential surface of thetubular portion, the seal gap being arranged to gradually increase inradial width with decreasing height.
 66. The fan according to claim 42,wherein the rotating portion includes a tubular portion arranged toextend downward and centered on the central axis, and arranged radiallyopposite an outer circumferential surface of the bearing portion; andthe seal gap is defined between an upper portion of the outercircumferential surface of the bearing portion and an innercircumferential surface of the tubular portion, the seal gap beingarranged to gradually increase in radial width with decreasing height.67. The fan according to claim 43, wherein the rotating portion includesa tubular portion arranged to extend downward and centered on thecentral axis, and arranged radially opposite an outer circumferentialsurface of the bearing portion; and the seal gap is defined between anupper portion of the outer circumferential surface of the bearingportion and an inner circumferential surface of the tubular portion, theseal gap being arranged to gradually increase in radial width withdecreasing height.
 68. The fan according to claim 44, wherein therotating portion includes a tubular portion arranged to extend downwardand centered on the central axis, and arranged radially opposite anouter circumferential surface of the bearing portion; and the seal gapis defined between an upper portion of the outer circumferential surfaceof the bearing portion and an inner circumferential surface of thetubular portion, the seal gap being arranged to gradually increase inradial width with decreasing height.
 69. The fan according to claim 45,wherein the rotating portion includes a tubular portion arranged toextend downward and centered on the central axis, and arranged radiallyopposite an outer circumferential surface of the bearing portion; andthe seal gap is defined between an upper portion of the outercircumferential surface of the bearing portion and an innercircumferential surface of the tubular portion, the seal gap beingarranged to gradually increase in radial width with decreasing height.70. The fan according to claim 46, wherein the rotating portion includesa tubular portion arranged to extend downward and centered on thecentral axis, and arranged radially opposite an outer circumferentialsurface of the bearing portion; and the seal gap is defined between anupper portion of the outer circumferential surface of the bearingportion and an inner circumferential surface of the tubular portion, theseal gap being arranged to gradually increase in radial width withdecreasing height.
 71. The fan according to claim 47, wherein therotating portion includes a tubular portion arranged to extend downwardand centered on the central axis, and arranged radially opposite anouter circumferential surface of the bearing portion; and the seal gapis defined between an upper portion of the outer circumferential surfaceof the bearing portion and an inner circumferential surface of thetubular portion, the seal gap being arranged to gradually increase inradial width with decreasing height.
 72. The fan according to claim 48,wherein the rotating portion includes a tubular portion arranged toextend downward and centered on the central axis, and arranged radiallyopposite an outer circumferential surface of the bearing portion; andthe seal gap is defined between an upper portion of the outercircumferential surface of the bearing portion and an innercircumferential surface of the tubular portion, the seal gap beingarranged to gradually increase in radial width with decreasing height.73. The fan according to claim 49, wherein the rotating portion includesa tubular portion arranged to extend downward and centered on thecentral axis, and arranged radially opposite an outer circumferentialsurface of the bearing portion; and the seal gap is defined between anupper portion of the outer circumferential surface of the bearingportion and an inner circumferential surface of the tubular portion, theseal gap being arranged to gradually increase in radial width withdecreasing height.
 74. The fan according to claim 50, wherein therotating portion includes a tubular portion arranged to extend downwardand centered on the central axis, and arranged radially opposite anouter circumferential surface of the bearing portion; and the seal gapis defined between an upper portion of the outer circumferential surfaceof the bearing portion and an inner circumferential surface of thetubular portion, the seal gap being arranged to gradually increase inradial width with decreasing height.
 75. The fan according to claim 51,wherein the rotating portion includes a tubular portion arranged toextend downward and centered on the central axis, and arranged radiallyopposite an outer circumferential surface of the bearing portion; andthe seal gap is defined between an upper portion of the outercircumferential surface of the bearing portion and an innercircumferential surface of the tubular portion, the seal gap beingarranged to gradually increase in radial width with decreasing height.76. The fan according to claim 52, wherein the rotating portion includesa tubular portion arranged to extend downward and centered on thecentral axis, and arranged radially opposite an outer circumferentialsurface of the bearing portion; and the seal gap is defined between anupper portion of the outer circumferential surface of the bearingportion and an inner circumferential surface of the tubular portion, theseal gap being arranged to gradually increase in radial width withdecreasing height.
 77. The fan according to claim 1, wherein the thrustportion is arranged to extend radially outward from the upper portion ofthe shaft; the bearing portion includes an upward-facing thrust dynamicpressure bearing surface arranged to face upward in an axial direction;the annular surface is a downward-facing thrust dynamic pressure bearingsurface arranged axially opposite the upward-facing thrust dynamicpressure bearing surface; and the thrust dynamic pressure bearingportion is defined by the upward-facing and downward-facing thrustdynamic pressure bearing surfaces.
 78. The fan according to claim 2,wherein the thrust portion is arranged to extend radially outward fromthe upper portion of the shaft; the bearing portion includes anupward-facing thrust dynamic pressure bearing surface arranged to faceupward in an axial direction; the annular surface is a downward-facingthrust dynamic pressure bearing surface arranged axially opposite theupward-facing thrust dynamic pressure bearing surface; and the thrustdynamic pressure bearing portion is defined by the upward-facing anddownward-facing thrust dynamic pressure bearing surfaces.
 79. The fanaccording to claim 3, wherein the thrust portion is arranged to extendradially outward from the upper portion of the shaft; the bearingportion includes an upward-facing thrust dynamic pressure bearingsurface arranged to face upward in an axial direction; the annularsurface is a downward-facing thrust dynamic pressure bearing surfacearranged axially opposite the upward-facing thrust dynamic pressurebearing surface; and the thrust dynamic pressure bearing portion isdefined by the upward-facing and downward-facing thrust dynamic pressurebearing surfaces.
 80. The fan according to claim 4, wherein the thrustportion is arranged to extend radially outward from the upper portion ofthe shaft; the bearing portion includes an upward-facing thrust dynamicpressure bearing surface arranged to face upward in an axial direction;the annular surface is a downward-facing thrust dynamic pressure bearingsurface arranged axially opposite the upward-facing thrust dynamicpressure bearing surface; and the thrust dynamic pressure bearingportion is defined by the upward-facing and downward-facing thrustdynamic pressure bearing surfaces.
 81. The fan according to claim 77,wherein the rotating portion includes a tubular portion arranged toextend downward and centered on the central axis, and arranged radiallyopposite an outer circumferential surface of the bearing portion; andthe seal gap is defined between an upper portion of the outercircumferential surface of the bearing portion and an innercircumferential surface of the tubular portion, the seal gap beingarranged to gradually increase in radial width with decreasing height.82. The fan according to claim 78, wherein the rotating portion includesa tubular portion arranged to extend downward and centered on thecentral axis, and arranged radially opposite an outer circumferentialsurface of the bearing portion; and the seal gap is defined between anupper portion of the outer circumferential surface of the bearingportion and an inner circumferential surface of the tubular portion, theseal gap being arranged to gradually increase in radial width withdecreasing height.
 83. The fan according to claim 79, wherein therotating portion includes a tubular portion arranged to extend downwardand centered on the central axis, and arranged radially opposite anouter circumferential surface of the bearing portion; and the seal gapis defined between an upper portion of the outer circumferential surfaceof the bearing portion and an inner circumferential surface of thetubular portion, the seal gap being arranged to gradually increase inradial width with decreasing height.
 84. The fan according to claim 80,wherein the rotating portion includes a tubular portion arranged toextend downward and centered on the central axis, and arranged radiallyopposite an outer circumferential surface of the bearing portion; andthe seal gap is defined between an upper portion of the outercircumferential surface of the bearing portion and an innercircumferential surface of the tubular portion, the seal gap beingarranged to gradually increase in radial width with decreasing height.85. The fan according to any one of claims 1, wherein the radial dynamicpressure bearing portion includes: an upper radial dynamic pressurebearing portion; and a lower radial dynamic pressure bearing portionarranged below and spaced from the upper radial dynamic pressure bearingportion; and an upper end of each of the blades is arranged at a levellower than that of a center of pressure of the upper radial dynamicpressure bearing portion when the rotating portion is rotated.
 86. Thefan according to any one of claims 1, wherein the radial dynamicpressure bearing portion includes: an upper radial dynamic pressurebearing portion; and a lower radial dynamic pressure bearing portionarranged below and spaced from the upper radial dynamic pressure bearingportion; and an upper end of each of the blades is arranged at a levellower than that of a center of the upper radial dynamic pressure bearingportion.